Effects of nitrogen addition and drought on the relationship between nitrogen-and water-use efficiency in a temperate grassland

Background Nitrogen-and water-use efficiency(NUE and WUE)reflect the capacity of plants to take up and utilize resources in the environments.Although N deposition and drought are known to affect plant growth and persistence,it remains elusive how plants adjust NUE,WUE and their relationship to adapt to the concurrent N deposition and drought under the context of global change.We conducted a field experiment in a temperate grassland in Inner Mongolia,in which N addition(10 g m^(–2)yr^(-1)),drought(reduced 66%precipitation during growing season)and their combination were manipulated,and we explored the responses of both instantaneous(NUE_(INST)and WUE_(INST))and long-term(NUE_(LT)and WUE_(LT))WUE and NUE for six common plant species(Leymus chinensis,Stipa baicalensis,Thermopsis lanceolata,Potentilla bifurca,Thalictrum squarrosum,Klasea centauroide).Results Across all the six species,NUE_(INST)decreased and WUE_(INST)increased with both N addition and drought;NUE_(LT)decreased with both N addition and drought,while WUE_(LT)decreased with N addition and increased with drought.A significant interactive effect between N addition and drought was detected,in that,drought weakened the negative effect of N addition on WUE_(LT)and NUE_(LT),and N addition weakened the negative effect of drought on NUE_(LT),but enhanced the positive effect of drought on WUE_(LT).As a consequence,drought caused a trade-off between NUE and WUE,and N addition brought forth positive correlation between NUE and WUE.Meanwhile,the relationship between NUE and WUE varied among the species of different functional groups.Conclusions Our study demonstrated that NUE,WUE and their relationship play an important role in determining their responses and adaptability to changes in soil nitrogen and water availability induced by N deposition and drought.Our results shed light on the antagonistic,synergetic and neutral effects between nitrogen deposition and drought on resource use efficiency,and further clarified the different adaptability among species of different functional groups,which will conduce to a comprehensive understanding on the role of NUE and WUE in plant persistence and coexistence in grassland ecosystems.

Method for C/N ratio estimation using Mask R-CNN and a depth camera for organic fraction of municipal solid wastes

Fast assessment of the initial carbon to nitrogen ratio(C/N)of organic fraction of municipal solid waste(OFMSW)is an important prerequisite for automatic composting control to improve efficiency and stability of the bioconversion process.In this study,a novel approach was proposed to estimate the C/N of OFMSW,where an instance segmentation model was applied to predict the masks for the waste images.Then,by combining the instance segmentation model with the depth-camera-based volume calculation algorithm,the volumes occupied by each type of waste were obtained,therefore the C/N could be estimated based on the properties of each type of waste.First,an instance segmentation dataset including three common classes of OFMSW was built to train mask region-based convolutional neural networks(Mask R-CNN)model.Second,a volume measurement algorithm was proposed,where the measurement result of the object was derived by accumulating the volumes of small rectangular cuboids whose bottom area was calculated with the projection property.Then the calculated volume was corrected with linear regression models.The results showed that the trained instance segmentation model performed well with average precision scores AP_(50)=82.9,AP_(75)=72.5,and mask intersection over unit(Mask IoU)=45.1.A high correlation was found between the estimated C/N and the ground truth with a coefficient of determination R2=0.97 and root mean square error RMSE=0.10.The relative average error was 0.42%and the maximum error was only 1.71%,which indicated this approach has potential for practical applications.